Laser-induced breakdown spectroscopy; Femtosecond laser; Double-pulse; Enhancement mechanism;INDUCED BREAKDOWN SPECTROSCOPY; SIGNAL ENHANCEMENT; METALLIC SAMPLES; OPTICAL-EMISSION; ABLATION; NANOSECOND; SILICON; ALUMINUM; SINGLE; COPPER

A dual-wavelength femtosecond double-pulse laser is used to induce the Cu plasma spectroscopy in air. The laser wavelengths are a fundamental wavelength (800 nm) and a second harmonic wavelength (400 nm) from Ti:sapphire laser. The inter-pulse delay of double-pulse is from 300 ps to 160 ps. The observed spectral intensity is dependent on the inter-pulse delay of the dual-wavelength femtosecond double-pulse. We analyze the characteristics of the plasma temperature and the electron number density on the inter-pulse delay of double-pulse with two different wavelengths. For 800 nm + 400 nm, the spectral emission enhancement is based on more material ablation. For 400 nm + 800 nm, the enhanced mechanism is plasma reheating effect. This study will provide a better way to understand the mechanism of femtosecond double-pulse LIBS. (C) 2017 Elsevier Ltd. All rights reserved.

INDUCED BREAKDOWN SPECTROSCOPY; LASER-ABLATION; LIGHT FILAMENTS; PULSED-LASER; VAPOR PLUME; AIR; PROPAGATION; PLASMA; COPPER; EXPLOSION

High-peak-power fs-laser filaments offer unique characteristics attractive to remote sensing via techniques such as remote laser-induced breakdownspectroscopy (R-LIBS). The dynamics of several ablation mechanisms following the interaction between a filament and a solid determines the emission strength and reproducibility of target plasma, which is of relevance for R-LIBS applications. We investigate the space-and time-resolved dynamics of ionic and atomic emission from copper as well as the surrounding atmosphere in order to understand limitations of fs-filament-ablation for standoff energy delivery. Furthermore, we probe the shock front produced from filament-target interaction using time-resolved shadowgraphy and infer laser-material coupling efficiencies for both single and multiple filament regimes through analysis of shock expansion with the Sedov model for point detonation. The results provide insight into plasma structure for the range of peak powers up to 30 times the critical power for filamentation Pcr. Despite the stochastic nucleation of multiple filaments at peak-powers greater than 16 Pcr, emission of ionic and neutral species increases with pump beam intensity, and short-lived nitrogen emission originating from the ambient is consistently observed. Ultimately, results suggest favorable scaling of emission intensity from target species on the laser pump energy, furthering the prospects for use of filament-solid interactions for remote sensing.

INDUCED BREAKDOWN SPECTROSCOPY; DOUBLE-PULSE; OPTICAL-EMISSION; CAVITY CONFINEMENT; TEMPERATURE; IMPROVEMENT; SILICON

The effect of spatial confinement on femtosecond laser-induced Cu plasmas was investigated by time-resolved spectroscopy. The cylindrical cavities with various diameters (2 and 3 mm) and various heights (2, 3, and 4 mm) were placed on the sample surface. An obvious enhancement in the emission intensity of Cu atomic lines was observed when a cylindrical cavity was used to confine the femtosecond laser-induced Cu plasmas. The results showed that enhancement ratios in femtosecond laser-induced breakdown spectroscopy with spatial confinement varied with cavity diameters and atomic emission lines selected. The spatial confinement effect was not significantly influenced by the cavity height because the height of plasma plume is lower than the cavity height. The maximum enhancement ratio for the emission intensities of the Cu atomic lines was measured to be around 3 at a time delay of 3.5 mu s when the cavity diameter is 2 mm. The spectral enhancement is attributed to the compression of the plasma by the reflected shock wave. Published by AIP Publishing.

dental caries; ultra-short lasers; thermal effects; atomic spectroscopy;INDUCED BREAKDOWN SPECTROSCOPY; QUANTITATIVE-ANALYSIS; REPETITION-RATE; TISSUE; FLUORESCENCE; CARIES; LIBS; BONE; IDENTIFICATION; ENAMEL

The goal of this work is to investigate the thermal effects of femtosecond laser (fs-laser) ablation for the removal of carious dental tissue. Additional studies identify different tooth tissues through femtosecond laser induced breakdown spectroscopy (fsLIBS) for the development of a feedback loop that could be utilized during ablation in a clinical setting. Scanning Election Microscope (SEM) images reveal that minimal morphological damages are incurred at repetition rates below the carbonization threshold of each tooth tissue. Thermal studies measure the temperature distribution and temperature decay during laserablation and after laser cessation, and demonstrate that repetition rates at or below 10kHz with a laser fluence of 40 J/cm(2) would inflict minimal thermal damage on the surrounding nerve tissues and provide acceptable clinical removal rates. Spectral analysis of the different tooth tissues is also conducted and differences between the visible wavelength fsLIBS spectra are evident, though more robust classification studies are needed for clinical trans-lation. These results have initiated a set of precautionary recommendations that would enable the clinician to utilize femtosecond laser ablation for the removal of carious lesions while ensuring that the solidity and utility of the tooth remain intact. 

Femtosecond laser ablation; Laser induced breakdown spectroscopy (LIBS); Spectrochemical imaging; YBa2Cu3O7 (YBCO); Thin film;OPTICAL-EMISSION SPECTROMETRY; MASS-SPECTROMETRY; ABLATION; SURFACE; SAMPLES; LIBS; PULSES; IDENTIFICATION; METALS; DAMAGE

We investigate femtosecond laser-induced breakdown-spectroscopy (fs-LIBS) for the spectrochemical imaging of thin films with high spatial resolution. Chemical images are obtained by recording LIBS spectra at each site of 2D raster-scans across the samples employing one fs-laser pulse per site. The diffraction images of the Echelle spectrometer are binned to reduce the read-out time of the intensified CCD detector and to increase the stability of the emission signals against peak drifts in the echellograms. For copper thin films on glass the intensities of Cu I emission lines and the size of ablation craters vary non-monotonously with the film thickness h(Cu) = 5-500 nm. The emission efficiency, defined as the Cu I line intensity per ablated volume, strongly decreases for films thicker than the optical penetration depth. The Na I line intensity from glass increases exponentially with decreasing Cu film thickness. For yttrium barium copper oxide (YBCO) thin films on MgO various atomic and molecular emission lines of the laser-induced plasma are measured (film thickness h(YBCO) = 200-1000 nm). The obtained element (Y, Ba, Cu, Mg) and molecular (Y-O) fs-LIBS images match the structure of the micro-patterned YBCO films very well. The achieved lateral resolution delta r = 6 mu m is among the best values reported for spectrochemical LIBS imaging. (C) 2017 Elsevier B.V. All rights reserved.

SPECTROSCOPY; INTENSITY; LINES; WATER

Temporal behavior of the intensity of Ba I emission lines (413.24 and 553.55 nm) in plasma of optical breakdown induced by femtosecond laser pulses (800 nm, 45 fs, 0.82 mJ) on the surface of BaCl2 aqueous solution was experimentally studied as dependent on delay time t (d) relative to the breakdown onset. The maximum intensity of the Ba I (413.24 nm) line was observed at t (d) = 20 ns, while the intensity of the Ba I (553.55 nm) line reached a maximum at t (d) = 40 ns. At t (d) = 10 ns, the intensity of the Ba I (413.24 nm) line was almost three times as large as that of Ba I (553.55 nm) line (despite the about two orders of magnitude lower probability of spontaneous transition for the former line), which is explained by the recombination cascade. It is established that, in the subsystem of 5d6p (3) D (0) and 6s6p (1) P (0) levels, the Boltzmann distribution is not valid and the local thermodynamic equilibrium is absent.

GRADIENT-INDEX MICROLENSES; INTRAOCULAR LENSES; CONTACT-LENSES; POLY(METHYL METHACRYLATE); INDUCEDBREAKDOWN; FUSED-SILICA; WAVE-GUIDES; IN-VIVO; POLYMERS; INTERFEROMETRY

We describe the treatment of new hydrogels with nine different chemical compositions by femtosecond laser writing. The phase change induced in the wavefront when passing through the written areas was measured in all of these materials. The induced phase change is negative, which is attributed to the higher presence of water in the written regions and confirmed via Raman spectroscopy. The largest induced change in a single layer at 100 mm/s was -3.69 waves at 543 nm. These results show a strong dependence of the phase change on the concentration of some components and their molar ratio. We propose that some components are essential for the nonlinear energy absorption (""dopants""), while other components (""quenchers"") are essential in redirecting the absorbed energy to cause chemical reactions that profoundly change the polymer structure. (C) 2017 Optical Society of America

Laser-induced breakdown spectroscopy; femtosecond LIBS; fs-LIBS; amalgam; dental restoration; mercury;INDUCED BREAKDOWN SPECTROSCOPY; RESTORATIVE DECISION-MAKING; RESIN-BASED COMPOSITE; PERMANENT TEETH; DENTAL AMALGAM; GLASS-IONOMER; LONGEVITY; REPLACEMENT; TOXICOLOGY; MIGRATION

In this work the diffusion of mercury and other elements from amalgam tooth restorations through the surrounding dental tissue (dentin) was evaluated using femtosecond laser-induced breakdown spectroscopy (fs-LIBS). To achieve this, seven deciduous and eight permanent extracted human molar teeth with occlusal amalgam restorations were half-sectioned and analyzed using pulses from a femtosecond laser. The measurements were performed from the amalgam restoration along the amalgam/dentin interface to the apical direction. It was possible to observe the presence of metallic elements (silver, mercury, copper and tin) emission lines, as well as dental constituent ones, providing fingerprints of each material and comparable data for checking the consistence of the results. It was also shown that the elements penetration depth values in each tooth are usually similar and consistent, for both deciduous and permanent teeth, indicating that all the metals diffuse into the dentin by the same mechanism. We propose that this diffusion mechanism is mainly through liquid dragging inside the dentin tubules. The mercury diffused further in permanent teeth than in deciduous teeth, probably due to the longer diffusion times due to the age of the restorations. It was possible to conclude that the proposed femtosecond-LIBS system can detect the presence of metals in the dental tissue, among the tooth constituent elements, and map the distribution of endogenous and exogenous chemical elements, with a spatial resolution that can be brought under 100 mu m.